Howe and Underwood: The Genus Riella 222 



spores. The involucres are less globose and more pointed at the 

 apex than those of R. Cossoniana. Judging from two specimens 

 of R. Cossoniana collected by Professor Trabut, R. affinis has the 

 appearance of being a larger species with broader lamina, though 

 this might not appear from a comparison of the measurements 

 given above with those given by authors for A'. Cossoniana. Our 

 specimens of R. affinis are prostrate and more or less entangled 

 with mud and are so delicate and fragile that it is quite possible 

 that the measurements in the above description may fail to do full 

 justice to the height of the plant. It may be remarked that in 

 occasional capsules the spores though showing a well-developed 

 brown coloration have short spines or papillae much like those 

 of R. Cossoniana ; such spores are always smaller than is normal 

 for the species and are probably immature or else have ripened 

 under abnormal conditions. 



Our experiments in germinating the spores of Riella affinis 

 have been more successful than those with the spores of Riella 

 Americana, though they were not begun until December, 1902, 

 five and a half years from the date of collection of the specimens. 

 More than half of the spores experimented with germinated in a 

 few days by being placed on a piece of wet filter-paper in a glass 

 dish kept in a moist chamber at ordinary living-room tempera- 

 tures. The germ-tube in practically all cases emerges, as in R. 

 Americana, from the outer or more spiny face of the spore, usually 

 near its middle. The root-hair follows a little later, its lumen re- 

 maining continuous with that of the germ-tube. The length of the 

 germ-tube varies exceedingly. Finally, there appears in it a some- 

 what curved transverse wall with its convexity turned toward the 

 spore. The part above contains most of the starch grains and in 

 the course of time begins to show chlorophyll, cell-divisions mean- 

 while taking place as described above for R. Americana. The 

 length of the germ-tube from the spore-wall to the curved septum 

 has been observed to vary in different cases from 0.02-0.7 mm. 

 One or two root-hairs, in addition to the one which comes from 

 the base of the germ-tube, may spring out later from some part of 

 the filamentous stalk of the young gametophyte. The forms as- 

 sumed by the young gametophytes are extremely varied and are 

 doubtless determined to a considerable extent by the conditions of 



